Plant This, Not That
The Maple and Pear Tree Edition
Invasive plants don’t sprout their own warning labels, so sometimes they can be hard to ID. To wit: a few years back, the Bank of Canada caused a dust up by mistakenly printing currency emblazoned with the leaf of a Norway rather than a sugar maple. The sugar maple is Canada’s national tree and symbol, as represented on the country’s flag, whereas Norway maples are an invasive species throughout North America and a specific threat to said sugar maple. Oops.
To be fair, I’m not sure I could spot the difference between a Norway and a sugar maple out in the wild, but then I’m not the Bank of Canada. In any case, this little branding mixup points to the need for us gardeners to pay close attention to what we’re purchasing and planting. Just because your local nursery or big box store is marketing it to you in an attractive and well-priced display doesn’t mean it’s environmentally kosher. In fact, a lot of plants that are known to be invasive are still sold and planted extensively. Find more on the problem with invasive plants here.
So let’s get into it with a couple of troublemaker trees that are widespread in landscapes and widely available in stores – but shouldn’t be.
Invasive: Norway Maple (Acer platanoides)
Norway maples, native to Europe and western Asia, are valued for their hardiness and tolerance of adverse conditions. They don’t mind concrete, soil compaction, pollution or salt, so they’re often included in urban and suburban landscapes.
They’ve long since escaped those parameters, though, aggressively taking over forests. They’re now considered invasive throughout the northeastern U.S. from Maine west to Wisconsin and south to Tennessee and Virginia, and also in the Pacific northwest. Their leaves open earlier in the spring, and drop later in the fall, than those of their native counterparts. They also have very shallow roots and their thick leaves produce dense shade, which prevents seedlings of native oaks, pines and maples from regenerating. They’re also prolific at spreading their own seeds around. While intact forests are generally able to withstand invaders, they seem to have few defenses against Norway maples, which have proven as effective at establishing themselves in mature forests as in cityscapes. Those North American forests in which Norway maples now dominate are considered “green deserts,” because native insects, birds and mammals struggle to survive there. Sixteen states – including all of New England and the mid-Atlantic from Maine to Virginia, as well as Oregon – have placed Norway maples on lists of noxious weeds and/or passed laws to prohibit or restrict their use.
Native Alternatives: Rocky mountain, bigleaf, sugar, red, scarlet, swamp and box elder maples (Acer glabrum, A. macrophyllum, A. saccharum, A. rubrum and A. negundo), among others.
There is no shortage of native species to meet your maple needs, whether you’re in Tampa, FL, Tacoma, WA or anywhere in between. They’re relatively fast-growing and thrive in a wide range of conditions. They offer cooling shade. They’re pollinator powerhouses, larval hosts to multiple caterpillars, and attractive to songbirds. Plus, they put on an annual fall foliage fireworks display. Some species even produce a delicious syrup that I’m told pairs well with pancakes. Hard to go wrong.
Invasive: Callery Pear (Pyrus calleryana)
Callery pear trees and their cultivars, including the prevalent Bradford type, have a neat oval shape, white flowers that blossom early in the spring, and attractive fall foliage. They’re also fast growing. These attributes have made them favorites of landscapers and homeowners, particularly since the 1960s.
Native to China, they produce huge volumes of seed, which get dispersed by birds and possibly small mammals. Their seedlings germinate and grow rapidly in disturbed areas, and they lack any real natural controls, such as insects and diseases. A single tree can spread rapidly by seed and vegetative means, forming a sizable patch within several years. Once established, callery pears form dense thickets that push out other plants, including native species that can’t tolerate the deep shade or compete for water, soil and space. Seeds in the ground can remain viable for up to ten years, making them difficult to eradicate. Fourteen states have included callery pears on warning lists or in restrictive laws.
Native Alternatives: downy serviceberry, sweet crabapple, wild plum, hollyleaf cherry, Mexican plum, beach plum, flowering dogwood, and eastern redbud (Amelanchier arborea, Malus coronaria, Prunus americana, Prunus ilicifolia, Prunus mexicana, Prunus maritima, Cornus florida, Cercis canadensis), among many, many others.
If you’re looking for a native tree that puts on an early-spring flower show, you’re in luck. Whatever ecoregion you live in, there are dozens to choose from – many of them overlooked and underutilized. Their nectar attracts bees, while their fruits attract birds and other mammals (including humans). A serviceberry, for example, hosts 19 species of native caterpillars. Many of these beauties also offer attractive fall foliage. What’s not to love?
Remember: when you plant native trees, you’re adding beauty while regenerating biodiversity. What a great way to do a bit of good for the world at a time when it’s easy to feel helpless.
Ok, so no discussion of maple leaves would be complete without a rendition of Scott Joplin’s ragtime classic, performed in this case on a French Quarter street corner by New Orleans’ one and only Tuba Skinny and recorded, apparently, by a lucky tourist (not me!).
Resources
Jill Swearingen, et. al., Plant Invaders of Mid-Atlantic Natural Areas, 4th edition, National Park Service and U.S. Fish and Wildlife Service, 2010.
Invasive Plant Atlas of the United States, University of Georgia and National Park Service.
Callery Pear Alert, Blue Ridge Prism, 2021.
Peter Kuitenbrouwer, “The Norway Maple Is a Bully, and Shouldn’t Be Confused with the Sugar Maple Tree,” The Globe and Mail, June 26, 2020.